1. Field of the Invention
The present invention relates to an abrading machine and, in particular, to an endless belt abrading machine wherein an endless belt is rotatably driven and brought into contact with a workpiece to be abraded.
2. Description of the Related Art
In a conventional endless belt abrading machine, when an operator wishes to abrade a workpiece, s/he holds the machine with either a left or right hand, and brings the belt of the machine into contact with a workpiece to be abraded. Conventional endless belt abrading machines are provided with an air motor having a rotation shaft extending in a direction transverse to the machine; and are also provided with a drive pulley, which is drivingly connected to a left end of the rotation shaft; with a driven pulley positioned forward of and spaced apart from the drive pulley; and with an endless belt which is engaged with and extends between the drive and driven pulleys. During operation, an operator generally holds the machine using his/her right hand. Operating the machine in this manner, it is relatively easy for the operator to observe a workpiece being abraded, since the endless belt is positioned to the left of the operator's right hand which is holding the machine. However, in a case that an operator is left-handed and uses his/her left hand to hold the machine at its rear end, it is difficult for the operator to observe a workpiece being abraded since the belt abrading the workpiece is positioned to the left of the operator's left hand which is holding the machine. Consequently, it is difficult for a left-handed person to effectively operate the machine.
To solve the drawback of the conventional art, there has been proposed an endless belt abrading machine which is adapted to be used upside down, or to be used wherein a position of a holding portion of the machine is changed from a left to right side relative to an endless belt of the machine. (For example, refer to Japanese Patent Application No. 2002-220567). One of the features of the machine of the prior invention is that when the machine is operated with a holding portion being shifted from a right to a left side, a direction of the motor's rotation can be reversed, thus enabling the abrasion belt to be driven in the same direction as that in which an operator is facing. Consequently, sparks which are generated upon abrading a workpiece move in a direction away from the operator, thus enabling an abrasion operation to be easily and safely carried out.
In the machine of the prior invention, a ring valve is mounted on an outer surface of the machine, and functions as a valve controller for starting and stopping rotation of the machine's air motor. To achieve this function, however, the ring valve must be manually moved in either a forward or rearward direction by an operator, which requires use of both of the operator's hands. Moreover, if it is desired to set a holding portion from a right to a left side in the machine of the prior invention, the entire machine must be turned upside down. Consequently, in a case, for example, where an indicator showing a degree of load is mounted on an outer surface of the machine, setting a holding portion of the machine from a right to a left side results in a drawback that the indicator is visually obscured.